1. Field of the Invention
The present invention relates to a stencil printing machine wherein printing is conducted by a printing drum having a stencil sheet wrapped thereon. More specifically, the stencil printing machine is such that an ink container detachably attached to the printing drum is lightened by lightening means to facilitate maintenance operation.
2. Description of the Related Art
FIG. 7 is a perspective view illustrating a printing drum detachably attached to a stencil printing machine.
After a front cover of the stencil printing machine is opened, the printing drum 50 is mounted therein. An ink container 51 is detachably attached to an approximately center position inside the printing drum 50. The ink container 51 stores ink therein.
FIG. 8 is a perspective view illustrating a constitution of ink supplying means 55 in the printing drum 50. This drawing is a view seen in a direction approximately opposite to that of FIG. 7, namely having a viewpoint in a rear side of the machine.
An ink motor 56 sucks ink stored in the ink container 51 and supplies the ink onto a squeegee roller 58 through plural holes formed in a tube-like distributor 57.
A doctor roller 59 is situated adjacent to the squeegee roller 58 at a small distance, i.e. a gap, away from the squeegee roller.
As shown in a front view of FIG. 9, the ink is accumulated to a predetermined quantity between the squeegee roller 58 and the doctor roller 59, thereby forming an ink swirl "A" with a uniform thickness while being rotated by a mixing shaft 60 situated therein.
The ink is conveyed along a circumferential surface of the squeegee roller 58 and supplied to an inner surface of the printing drum 50 contacting the squeegee roller 58, and then allowed to pass through the drum to transfer to an outer surface. Around the outer surface of the printing drum, a stencil sheet perforated according to an image is wrapped. The ink passes through perforations of the stencil sheet to transfer onto a printing sheet, thereby forming a predetermined image thereon.
The ink supplying means 55 has an ink sensor 63 used for stabilizing ink supply from the ink container 51.
The ink sensor 63 is attached to a board 65 situated above the ink swirl "A" inside the printing drum 50. The ink sensor 63 has two needle-shaped electrodes, a long one 63b and a short one 63a, each extending downwards from the board 65 for detecting quantity of the ink.
When the ink is supplied to the printing drum 50 through the squeegee roller 58 during printing, suction by the ink motor 56 is controlled so that quantity of ink in the ink swirl "A" is kept constant while being detected by the electrode 63b or 63a between two end-points thereof.
As described above, the ink supplying means 55 is situated inside the printing drum 50. Consequently, the ink container 51 must be detached from the printing drum when an operator is required to see a position of the ink swirl "A" in order to conduct a performance test of the ink supplying means 55 during assembling the machine and an in-serve maintenance operation. And, the operator is forced to see the position through a narrow access opening comparable to a diameter of the ink container 51.
Conventionally, the operator manages to conduct the maintenance operation, lightening the position by a flashlight from outside the machine; however, lightening the position is difficult to conduct properly, and the operation itself is not easy since one hand of the operator is occupied by the flashlight. Further, temperature inside the printing drum 50 is expected not to fluctuate as long as possible. Namely, fluctuation of the temperature inside the printing drum 50 changes viscosity of the ink, thereby finally affecting printing quality.
The present invention is made to solve the aforementioned problems. An object of the present invention is to provide a stencil printing machine such that an operator can see the inside of the printing drum easily without affecting temperature thereof, and a life-time of lightening means for lightening a position to be checked can be effectively used.